Hydrosilylation chemistry, typically involving a reaction between a silyl hydride and an unsaturated organic group, is one basic route in the synthesis of commercial silicone-based products like silicone surfactants, silicone fluids and silanes, as well as many addition cured products like sealants, adhesives, and silicone-based coating products. Heretofore, hydrosilylation reactions have been typically catalyzed by precious metal catalysts, such as platinum or rhodium metal complexes.
Various precious metal complex catalysts are known in the art. For example, U.S. Pat. No. 3,775,452 discloses a platinum complex containing unsaturated siloxanes as ligands. This type of catalyst is known as Karstedt's-catalyst. Other exemplary platinum-based hydrosilylation catalysts that have been described in the literature include Ashby's catalyst as disclosed in U.S. Pat. No. 3,159,601, Lamoreaux's catalyst as disclosed in U.S. Pat. No. 3,220,972, and Speier's catalyst as disclosed in Speier, J. L, Webster J. A. and Barnes G. H., J. Am. Chem. Soc. 79, 974 (1957).
Although these precious metal complex catalysts are widely accepted as catalysts for hydrosilylation reactions, they have several distinct disadvantages. One disadvantage is that the precious metal complex catalysts are inefficient in catalyzing certain reactions. For example, in the case of hydrosilylations of allyl polyethers with silicone hydrides using precious metal complex catalysts, use of an excess amount of allyl polyether, relative to the amount of silicone hydride, is needed to compensate for the lack of efficiency of the catalyst in order to ensure complete conversion of the silicone hydride to a useful product. When the hydrosilylation reaction is completed, this excess allyl polyether must either be: (A) removed by an additional step, which is not cost-effective, or (B) left in the product which results in reduced performance of this product in end-use applications. Additionally, the use of an excess amount of allyl polyether typically results in a significant amount of undesired side products such as olefin isomers, which in turn can lead to the formation of undesirably odoriferous byproduct compounds.
Another disadvantage of the precious metal complex catalysts is that sometimes they are not effective in catalyzing hydrosilylation reactions involving certain type of reactants. It is known that precious metal complex catalysts are susceptible to catalyst poisons such as phosphorous and amine compounds. Accordingly, for a hydrosilylation involving unsaturated amine compounds, the precious metal catalysts known in the art are normally less effective in promoting a direct reaction between these unsaturated amine compounds with Si-hydride substrates, and will often lead to the formation of mixtures of undesired isomers.
Further, due to the high price of precious metals, the precious metal-containing catalysts can constitute a significant proportion of the cost of silicone formulations. Recently, global demand for precious metals, including platinum, has increased, driving prices for platinum to record highs, creating a need for effective, low cost replacement catalysts.
Silahydrocarbons contain only carbon, hydrogen and silicon atoms, and are useful in a variety of industrial applications. For example, tetraalkylsilanes, wherein two or more of the alkyl groups have between eight and twenty carbon atoms, have been shown to be useful and effective hydraulic fluids and lubricants, especially in aerospace and space vehicles. Pettigrew (Synthetic Lubricants and High Performance Fluids (second edition), L. R. Rudnick and L. R. Shubkin (Editors), Marcel Dekker, NY 1999, PP 287-296) has reviewed various methods for synthesizing these fluids, many of which rely on hydrosilylation, catalyzed by precious metal catalysts (Rh, Pt, Pd) for hydrosilylation of alpha olefins by primary, secondary, and tertiary silanes. Specific disclosures of such syntheses using precious metal catalysts include the following:
U.S. Pat. No. 4,572,971 disclosed the rhodium-catalyzed hydrosilylation synthesis of saturated and unsaturated silahydrocarbons from alpha olefins and dialkylsilanes and/or trialkylsilanes. Completely saturated silahydrocarbon products were obtained by hydrogenation of the unsaturated silahydrocarbons byproducts.
U.S. Pat. No. 4,578,497 disclosed the platinum-catalyzed hydrosilylation of alpha olefins with primary (—SiH3), secondary (═SiH2) and tertiary (≡SiH) silanes to produce a reaction mixture still containing unreacted SiH functionality and subsequently introducing air or oxygen to complete the conversion to the tetraalkylsilane.
Lewis, et al., (Organometallics 9 (1990) 621-625) reported that both rhodium and platinum colloids catalyze the hydrosilylation synthesis of CH3(C10H21)Si(C8H17)2 from CH3(C10H21)SiH2 and 1-octene. Rhodium was more active than platinum and injection of air or oxygen was critical to obtaining complete conversion of the starting materials to the silahydrocarbon. The primary (—SiH3) and secondary silanes (═SiH2) inhibited the platinum catalysis, but no inhibition was observed with rhodium.
LaPointe, et al., (J. Amer. Chem. Soc., 119 (1997) 906-917) reported the palladium-catalyzed hydrosilylation synthesis of tetralkylsilanes from tertiary silanes and olefins.
Bart, et al (J. Amer. Chem. Soc., 126 (2004) 13794-13807) reported that the bis(imino)pyridine iron di-nitrogen compound (iPrPDI)Fe(N2)2 [iPrPDI=2,6-(2,6-(iPr)2-C6H3N═CMe)2C5H3N] was an effective catalyst for hydrosilylation of alkenes and alkynes by primary and secondary silanes. However, the reaction products always had one or two SiH bonds and no tetraalkylsilanes were observed.
U.S. Pat. No. 8,236,915 discloses the use of manganese, iron, cobalt and nickel complexes of terdentate pyridine diimine ligands as hydrosilylation catalysts. However, this reference does not disclose use of these catalysts in the production of unsaturated silahydrocarbons.
Trisilahydrocarbon compounds are disclosed in U.S. Pat. No. 4,788,312. They are synthesized by a method comprising (1) Pt-catalyzed hydrosilylation of a large molar excess of alpha, omega dienes of four to sixteen carbon atoms by dihalosilanes to yield bis(alkenyl)dihalosilanes, and (2) further hydrosilylation of the bis(alkenyl)dihalosilanes by a trialkylsilane, or (3) further hydrosilylation of the bis(alkenyl)dihalosilanes by a trihalosilane and (4) substitution of the halogen atoms by reaction with Grignard, organolithium or organozinc reagents.
U.S. Pat. Nos. 5,026,893 and 6,278,011 disclose polysilahydrocarbons by methods comprising Pt-catalyzed hydrosilylation of substrates such as alkyltrivinylsilanes, phenyltrivinylsilane or trivinylcyclohexane with trialkylsilanes. The hydrosilylation methods disclosed are unreactive with internal olefins (See U.S. Pat. No. 6,278,011, Column 4, lines 2-6).
As an alternative to precious metals, recently, certain iron complexes have gained attention for use as hydrosilylation catalysts. Illustratively, technical journal articles have disclosed that that Fe(CO)5 catalyzes hydrosilylation reactions at high temperatures. (Nesmeyanov, A. N. et al., Tetrahedron 1962, 17, 61), (Corey, J. Y et al., J. Chem. Rev. 1999, 99, 175), (C. Randolph, M. S. Wrighton, J. Am. Chem. Soc. 108 (1986) 3366). However, unwanted by-products such as the unsaturated silyl olefins, which result from dehydrogenative silylation, were formed as well.
A five-coordinate Fe(II) complex containing a pyridine di-imine (PDI) ligand with isopropyl substitution at the ortho positions of the aniline rings has been used to hydrosilylate an unsaturated hydrocarbon (1-hexene) with primary and secondary silanes such as PhSiH3 or Ph2SiH2 (Bart et al., J. Am. Chem. Soc., 2004, 126, 13794) (Archer, A. M. et al. Organometallics 2006, 25, 4269). However, one of the limitations of these catalysts is that they are only effective in hydrosilylating the aforementioned primary and secondary phenyl-substituted silanes, and not in hydrosilylating tertiary or alkyl-substituted silanes such as Et3SiH, or with alkoxy substituted silanes such as (EtO)3SiH.
Other Fe-PDI complexes have also been disclosed. U.S. Pat. No. 5,955,555 discloses the synthesis of certain iron or cobalt PDI dianion complexes. The preferred anions are chloride, bromide and tetrafluoroborate. U.S. Pat. No. 7,442,819 discloses iron and cobalt complexes of certain tricyclic ligands containing a “pyridine” ring substituted with two imino groups. U.S. Pat. Nos. 6,461,994, 6,657,026 and 7,148,304 disclose several catalyst systems containing certain transitional metal-PDI complexes. U.S. Pat. No. 7,053,020 discloses a catalyst system containing, inter alia, one or more bisarylimino pyridine iron or cobalt catalyst. However, the catalysts and catalyst systems disclosed in these references are described for use in the context of olefin polymerizations and/or oligomerisations, not in the context of hydrosilylation reactions.
There is a continuing need in the hydrosilation industry for selectively catalyzing hydrosilylation reactions, particularly those involving silahydrocarbons such as tetraalkylsilanes from alkenes and primary and/or secondary silanes. A method of producing silahydrocarbons catalyzed by compounds of non-precious transition metals such as manganese, iron, cobalt and nickel, would be useful in the industry. The present invention provides one answer to that need.